This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A247822 #25 Feb 26 2025 05:53:15 %S A247822 7,8191,8191,131071,524287,524287,2147483647,2147483647, %T A247822 2305843009213693951,2305843009213693951,2305843009213693951, %U A247822 2305843009213693951 %N A247822 Corresponding values of primes p from A247821 and A247838. %C A247822 Conjecture: all terms are Mersenne primes (A000668). %C A247822 Conjecture: next terms are 2305843009213693951, 2305843009213693951, 2305843009213693951, 2305843009213693951 and 618970019642690137449562111. - _Jaroslav Krizek_, Mar 25 2015 %F A247822 a(n) = sigma(sigma(2*A247821(n)-1)) = A000203(A000203(2*A247821(n)-1)) = A051027(2*A247821(n)-1). %F A247822 a(n) = sigma(sigma(A247838(n))) = A000203(A000203(A247838(n))) = A051027(A247838(n)). %e A247822 a(2) = 8191 because sigma(sigma(2*A247821(2)-1)) = sigma(sigma(A247838(2))) = 8191. %o A247822 (Magma) [SumOfDivisors(SumOfDivisors(n)): n in [A247838(n)]]; %Y A247822 Cf. A000203, A008438, A247790, A247791, A247820, A247821, A247823, A247954. %K A247822 nonn,more %O A247822 1,1 %A A247822 _Jaroslav Krizek_, Sep 28 2014 %E A247822 a(7)-a(8) from _Jaroslav Krizek_, Mar 25 2015 %E A247822 a(9)-a(12) from _Giovanni Resta_, Feb 14 2020